Chan also had a busy week, graduating from medical school on Monday, as Zuckerberg marked his 28th birthday.

The guests believed they were going to celebrate Chan's graduation - but found they were at a wedding instead.

The wedding ring, a "very simple ruby", was designed by Zuckerberg.

Nine years ago the pair met at Harvard, where Zuckerberg founded Facebook in 2004.

They later moved to California, where Facebook has its headquarters, and Chen studied at the medical school of the University of California, San Francisco.

On Monday, Zuckerberg turned 28 and Chan graduated from the University of California, San Francisco School of Medicine, where she'd studied pediatrics.

Then on Friday, Zuckerberg took his blue-and-white web behemoth public in one of the most anticipated stock offerings in Wall Street history.

The seemingly well-coordinated timing was largely a coincidence, the guest said. The wedding had been planned for months and the couple was waiting for Chan to finish medical school, but the date of the IPO was a "moving target" not known when the wedding was set.

Attendees, including Facebook's chief operating officer Sheryl Sandberg, were told after they arrived that they were not mere party guests but wedding guests.

"Everybody was shocked," the guest said.

The person would not discuss the names of others who attended to protect their privacy.

Ditching his trademark hoodie and sneakers, Zuckerberg sported a dark blue suit and tie with a white shirt for the ceremony, while Chan wore a traditional white wedding dress with veil and lace.

Food was served family-style and included dishes from the couple's favorite Palo Alto sushi restaurant.

Zuckerberg met Chan at Harvard, where he founded Facebook in a dorm room in 2004, and have been together for more than nine years.

Chan's own Facebook page, which now lists her as married to the founder, said she is a native of Braintree, Mass., and attended high school in nearby Quincy.

She graduated Harvard in 2007 then taught science to fourth and fifth graders at the Harker School in San Jose for two years before starting medical school, according to her profile.

Her page also says she "loves cooking and soft things."

Even after the IPO, Zuckerberg, who grew up in Dobbs Ferry, N.Y., remains Facebook's single largest shareholder, with 503.6 million shares, and he controls the company with 56% of its voting stock.

The site has grown into a worldwide network of almost a billion people and made its founder, Time magazine's Person of the Year in 2010, one of the most famous businessmen of the Internet age.

Facebook's valuation after its flotation on Friday means the social network site is worth about the same as internet shopping giant Amazon, and more than the value of stalwarts such as Disney.

Even after the flotation, Zuckerberg continues to control just under 56% of the voting power of the company.

Zuckerberg "Likes" Chan and Weds

In a quiet backyard celebration Mark Zuckerberg, CEO of Facebook married his long-time girlfriend, Pricilla Chan at his home in Palo Alto, CA today. Guests were told they were celebrating Chan’s graduation from medical school and were shocked to learn that the event was actually a wedding. The bride graduated from University of California San Francisco with a doctorate earlier this week, on the same day as Zuckerberg’s birthday. About 100 guests attended the affair.

Zuckerberg tipped off the press to the nupials when he changed his status to “married” on his Facebook page. He shared the photo above on his Facebook page and on his timeline, along with a photo from the stock exchange. AP reported the story.

The bride wore an elegant long, white wedding dress with a delicate lace overlay. The wedding ring was simple ruby, designed by Zuckerberg. The groom wore a serious dark suit with a narrow tie, not his casual garb with his signature hoodie.

The wedding was the final ceremony of a bruising week that included the highly-anticipated IPO of Facebook, which broke records on market capitalization for internet companies.

The couple dated for eight years before the wedding. They met at Harvard University when Facebook was in its early phases. They had been planning the wedding for months and decided to wait until after Chan graduated. The timing was not related to the date of Facebook IPO, which had been in flux for weeks due to SEC delays. Zuckerberg turned 28 this week and Chan is 27.